Due to ease of accessibility, tumor cell surface antigens are invaluable targets for therapeutic development. The epitope space at the cell surface is highly complex. Relevant antigens may include glycosylated proteins and other post-translationally modified products that may not be readily predicted from studies of genomic copy number or mRNA expression levels (Liu et al. (2004) Cancer Res. 64: 704-710; Kobata and Amano (2005) Immunol. Cell Biol. 83: 429-439; Birkle et al. (2003) Biochimie (Paris) 85: 455-463; Hakomori (2001) Adv. Exp. Med. Biol. 491: 369-402; Hanisch, F. G. (2001) O-Glycosylation of the mucin type. Biol. Chem. 382, 143-149; Ugorski and Laskowska (2002)Acta Biochim. Pol. 49: 303-311).
Because monoclonal antibodies (mAbs) recognize a wide range of antigenic determinants with high affinity and specificity and are able to discern subtle differences in antigen structure and conformation, they can be used to efficiently map the tumor cell surface epitope space (Liu et al. (2004) Cancer Res. 64, 704-710). Isolating these epitopes enables the antibodies to achieve specific binding to neoplastic cells, an ability that could be utilized in applications such as induction of antibody-dependent cell cytotoxicity (Clynes et al. (2000) Nat. Med 6: 443-446) or inhibition of signaling pathways involved in tumor cell migration, growth, and survival (McWhirter et al. (2006) Proc. Natl. Acad. Sci., USA, 103: 1041-1046; Fuh et al. (2006) J. Biol. Chem. 281: 6625-6631). In addition, antibodies targeting internalizing tumor epitopes could be exploited to achieve efficient and specific intracellular delivery of chemotherapeutic drugs and/or other tumor-modulating agents (Liu et al. (2004) Cancer Res. 64: 704-710; Nielsen et al. (2002) Biochim. Biophys. Acta 1591: 109-118; Pirollo et al. (2006) Hum. Gene Ther. 17: 117-124; Song et al. (2005) Nat. Biotechnol. 23:709-717; Liu et al. (2002) J. Mol. Biol. 315: 1063-1073).
Phage antibody display has been widely used to develop cancer-specific antibodies (Liu et al. (2004) Cancer Res. 64: 704-710; Liu and Marks (2000) Anal. Biochem. 286: 119-128; 15. Marks et al. (1992) Biotechnology (N.Y.) 10: 779-783; Marks et al. (1991) J. Mol. Biol. 222: 581-597; Marks et al. (1992) J. Biol. Chem. 267: 16007-16010; Sharon et al. (2005) J. Cell. Biochem. 96: 305-313; Silacci et al (2005) Proteomics 5: 2340-2350; Gao et al. (2003) J. Immunol. Methods 274: 185-197; Lekkerkerker and Logtenberg (1999) J. Immunol. Meth., 231: 53-63; de Kruif et al. (1995) Proc. Natl. Acad. Sci., USA, 92: 3938-3942; Pini et al. (1998) J. Biol. Chem. 273: 21 769-21 776). A combinatorial phage antibody library serves as a source of random shape repertoire that can be used to probe neoplastic variations on the surface of cancer cells (Liu et al. (2004) Cancer Res. 64: 704-710; Geuijen et al. (2005) Eur. J. Cancer 41: 178-187; Poul et al. (2000) J. Mol. Biol. 301: 1149-1161; Cai and Garen (1995) Proc. Natl. Acad. Sci., USA, 92: 6537-6541). Selecting phage antibody libraries directly on cancer cell lines enables the identification of tumor-targeting antibodies without prior knowledge of target antigens (Liu et al. (2004) Cancer Res. 64: 704-710; Gao et al. (2003) J. Immunol. Methods 274: 185-197; Geuijen et al. (2005) Eur. J. Cancer 41: 178-187; Poul et al. (2000) J. Mol. Biol. 301: 1149-1161). Although numerous antibodies have been found by this approach, the screening process against cell lines does not provide an ideal picture as to how specific these antibodies will be to actual cancer cells in patient populations. After several generations in culture, cancer cell lines may express cell surface epitopes that differ from those present in the original cancerous tissue. Tissue sections from cancer patients would be an ideal selection target in the development of cancer-specific antibodies; however, most tissues taken during surgeries, biopsies, or autopsies are composed of heterogeneous cell populations. This seemingly poses a serious obstacle to selection methods that would specifically target cancer cells in tissue.